This invention relates to a thermally developing apparatus, and in particular, to a thermally developing apparatus wherein image formation is carried out by holding a thermally developable material on the outer circumferential surface of a heated drum.
A thermally developing apparatus has been developed which is capable of forming a visible image from an image which has been formed as a latent image by continuously supplying sheet-shaped thermally developable materials to the outer circumferential surface of a heated drum to cause a thermal reaction to occur in these thermally developable materials (refer to TOKUHYOHEI 10-500497 and TOKUHYOHEI 10-500506). According to these thermally developing apparatus, a sheet-shaped thermally developable material is supplied to the outer circumferential surface of a drum rotating at a constant rotational speed, and after the drum has rotated for a predetermined rotary angle with the thermally developable material being held, the thermally developable material is detached from the outer circumferential surface of the drum, while a new thermally developable material is simultaneously supplied to the outer circumferential surface of the drum; hence, it is possible to heat sheet-shaped thermally developable materials efficiently.
However, it has been proved that, in a thermally developing apparatus which heats a thermally developable material as it is held by a heating member controlled at a predetermined thermal development temperature (for example, the apparatus disclosed in TOKUHYOHEI 10-500497), when a thermally developable material having a different size from a preceding thermally developable material is thermally developed immediately after said preceding one is thermally developed, sometimes unevenness of density appears in the succeeding thermally developable material.
In respect of this, in the description of TOKUHYOHEI 10-500506, a thermally developing apparatus wherein temperature control is made for each of the regions, that is, the central portion of the drum and its both side regions is disclosed. However, in this prior art, the purpose of dividing the region for temperature control is to eliminate the temperature difference being produced in the central portion and its both sides owing to the cooling from both sides of the drum, and no disclosure or even no suggestion is done concerning the density unevenness which may appear in the case where thermally developable materials having different sizes from one another are supplied.